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Ventilation for a very small home

When we built our little home (720 sq ft, basically 2 main rooms) 13 yrs ago, we made it very tight and well insulated, but we did not take into account the need for makeup air. The first time we ran our dryer, we had air pulling in through the electrical outlets! We learned to always leave windows cracked open and we added a fan that pulls outdoor air into the laundry closet while the dryer is running. Here in the PNW, in the winter this brings in cold, damp air. I’ve been looking at ERVs but with a home this small and with very little free wall/ceiling space, would an ERV be a workable solution? Also is it something I could do myself?

One thing that I would like to see on this site is more advice for those with small homes. Everything seems geared to having a forced air furnace system which I don’t have. It wouldn’t make sense in a house this size and I’ve never cared for the kind of heat they give.

Anyways, thanks for any advice, I get so much good information here (albeit a little hard to decode at times).

Replies

In the PNW and elsewhere) old damp winter air is still usually much drier than the indoor air in absolute terms. Pulling that air indoors does not create a humidity problem, but it IS an energy & comfort problem. Unvented heat pump dryers would be one solution.

An ERV usually only makes sense in locations that have a fairly substantial latent cooling (outdoor humidity) problem in summer. In the PNW the latent loads are almost always NEGATIVE even when it's hot out. An HRV (sensible heat only) makes more sense in your climate.

ASHRAE 62.2 ventilation rates for a 720' house would be about 40 cfm for a 1-bedroom house, 5o cfm for a 2 bedroom, which would be half (or less) the cfm of a clothes dryer. But if half the dryer makeup air is coming from the HRV it's still better than pulling it through the electrical outlets (which is an indication of leaky house sheathing, BTW.)

If you are concerned about breathing polluted air (you should be), then add an HRV. It's not clear that you have any other problems. For example, what's wrong with cold air entering a closet, going into the dryer and then out?

L.H.,
A pair of Lunos fans are worth considering. More information here: "European Products for Building Tight Homes." (Scroll down to the section under the heading, "An intriguing new approach to heat-recovery ventilation.")

You should know, however, that HRVs, ERVs, and Lunos fans are not makeup air devices. They are balanced ventilation systems that exhaust the same volume of air as they supply. Manufacturers of HRVs and ERVs usually state this fact in their installation instructions, noting that these ventilation fans should not be used as a makeup air source.

A pair of Lunos fans is good for 22cfm, so it won't actually meet ASHRAE 62.2 ventilation rates with a single pair. But they're relatively easy to install as a retrofit.

Building Science Corporation believes ASHRAE 62.2 is too high anyway, and have proposed Floor Area x 0.01 + 7.5 (#bedrooms +1) for the ventilation cfm (ASHRAE uses Floor Area x 0.3). Under the BSC standard a 720' single bedroom house would need (720 x 0.1) + 7.5 x (1 + 1) = 22.5cfm, which is just 0.5cfm over ventilation rate of a single pair of Lunos, which should be "good enough".

That would also provide a makeup air path for the dryer WAY better than what you have going now.

It seems like you have two separate issues: the first one is makeup air for the dryer and the second is some type of continuous ventilation.

Don't most dryers need 100-200+ CFM? If that's the case, I think your options are existing laundry fan, windows, or get a condensing dryer. We have a LG combo washer/dryer that we're happy with, it would save you space and no need for venting. Before you go any further with house modifications for dryer makeup air, I'd seriously consider the no vent dryer options.

We run one of our bath fans 24/7 at 30 CFM for a 1300+ sq ft house and that seems like more than enough ventilation. For a small place like yours, I think anything over 30 CFM would be overkill. Your best options might be something from the Lunos product line: either one pair of the E2, and eGo or two, or even their low volume exhaust fan (if you don't have a bath fan): https://foursevenfive.com/products/ventilation/

Brian, another option is passive makeup air. Its pros and cons are debated regularly on GBA but after going through all of the options on a current project, I ended up spec'ing a Panasonic bath fan that will run continuously, and a Lunos makeup air kit that will allow fresh air in if the building depressurizes: https://foursevenfive.com/lunos-ald-r160-passive-air-inlet-kit/.

Yes, we ended up installing 4 Panasonic passive air inlets in our very well air sealed house (.38 ACH 50 final blower door) so the WhisperGreen fan at 30 CFM can get enough air. When boosted to 80 CFM, the fan still de-pressurizes the house, even with all 4 inlets wide open. We actually have two WhisperGreen fans, one in each bathroom, but only run one 24/7.

We initially installed 2 passive air inlets because the specs say up to 18 CFM, but that is wrong, the reality seems like they are only capable of 10 CFM. The Lunos make up air kits look nice, but 4x the cost of the Panasonic.

I don't think the exhaust fan with make up air is great in our cold climate because the house gets a bit dry in the winter, but it's probably fine in the PNW. If building again, I would go small HRV or consider Lunos.

Someday, I might consider swapping out the two Panasonic bath fans for two Lunos exhaust fans. That way, I could run both fans 24/7 and I'd probably run them each at 9 CFM in cold winter weather.

There is a gap in the market for balanced ventilation for small homes. As far as I can tell it's currently filled only by Lunos. They are well-made and energy efficient, but they are not completely silent; they turn off and on again every 55-75 seconds, which sensitive people can find annoying. Zehnder has a couple of small units but they are not available in the US. It would be great if other manufacturers would offer continuous ventilation with very low CFM.

There are several models with a max output around 60CFM. With multi-speed controls, and/or 20/40/60 operation, it would be very easy to get effectively 20CFM or below. The cost of these is in the few hundred dollar range.

I see. For a home this small, I wouldn't think you'd need air directly into the bedroom. If it was really deemed necessary, I would still default to a small HRV with ECM motors. Lifebreath has 5 speed fan controllers, so getting down to sub 20CFM should be a trivial matter. My Zehnder's "away" mode defaults to about 18CFM, and in that mode it would have to be completely silent in the room for me to tell if it's on at all, or powered off from 3 feet away. Once I dialed it back to about 10CFM, I literally can't hear it run.

"which sensitive people can find annoying."
Wow, that's sensitive! With my sones meter, traffic on the street is 100 times louder with all windows closed. Placement of the Lunos may be critical in that case. They are about 30 times quieter than air passing through a floor register with a standard furnace blower.

What are the actual readings you're getting those numbers from? They don't seem reasonable to me. A typical air register would be on the order of 30-40dB, which is about 0.5-1 sone. 30 times less than that, and you're into super-human hearing territory, like the sound of someone breathing in the next room. And the street noise, with the windows closed, is 100 times louder than a fan inside the house? Unless you have paper walls, and wear 25dB ear plugs all day, I'm having a hard time buying that.

Yesterday I talked with a client who has been living with two pairs of Lunos E2 and a Lunos Ego, and asked him about the noise. He said that if you pay attention you can hear it, but that it quickly dissolves into the background, at least for him.

Paul, I'm just reporting what I've noticed and what people who live with them have told me. I don't think Lunos would bother anyone in a living area, but inside a bedroom, sensitive sleepers can hear the fan change direction every 55-75 seconds. (55 for thin walls, 75 for thick walls.) They also put a hole in the wall, so if you have thick, cellulose-filled walls and triple-glazed windows, which block almost all sound, Lunos punch a hole in that envelope. I still think they're great, just not for every situation.

This is an interesting about the noise that I hadn't thought of. One thing about a well insulated home is that it's very quiet. I definitely get a clear path for outside noises through my bath fan- is it similar to that?

As asked above, I do have a good bath fan that I use every day and presently I just always leave a window cracked open to make up the air. The dryer, on the other hand, needs a lot of makeup air. I can't remember the amount but I remember when my husband and I were researching it with the specs, it was going to take a large window opening to provide enough air. This is why we went with the fan, which still is a bit lower than what the dryer needs, so I also keep a window cracked open. I really wish dryers were designed for direct vent, but although there is a main air intake, it actually pulls air in through any opening in the whole device.

Brian, I am interested in hearing more about your non-venting dryer. I have been reading up on these. Some people are very happy with them but the reviews are mixed. Long drying times, clothes coming out wrinkly, inability to lightly dry delicate items/clothes getting very hot, and frequent repairs are some of the complaints I've been reading about. How long have you had yours? Have you had any of these issues?

We've had our LG combo unit for 3+ years with no repair issues. We normally dry our clothes outside (or inside during the dry winter air). I can't say that wrinkles and drying delicate items have been an issue or something important to us.

We like it because it takes up less space than separate washer/dryer and didn't require a big hole in the house for vent (and makeup air issues). Those benefits make it worthwhile compared to a normal setup.

In your situation, it seems like switching to a ventless dryer (or combo unit) would be easier than making major ventilation changes.

For our Whirlpool WED99HEDW,
"Long drying times" - True, probably 20-30 minutes longer. We're never really in a rush to get our clothes, however when coupled with the fact that it's pretty noisy, this is a negative. If you can put it away from the living areas, it's not an issue. We have it in our upstairs bathroom, and while I wish it was quieter, I wouldn't trade it. A regular dryer isn't exactly quite either.
"clothes coming out wrinkly" - No. Same or less wrinkly than prior dryers I've used.
"inability to lightly dry delicate items/clothes getting very hot" - This doesn't make a whole lot of sense to me; there's nothing inherent about the technology that would make this the case. Almost all of europe uses this type of dryer, and I'm pretty sure they didn't abandon delicate clothing items as a result. One model or another might be better or worse at this particular task.
"frequent repairs" We haven't had ours long enough to say how reliable it is. The fear of a breakdown is real, if only due to the fact that repair support is going to be next to zero. I'd be surprised if there's a repair shop within 200 miles of me who's even heard of a heat pump dryer, let alone worked on one. This is one case where I would have bought an extended warranty, if it was available.

I’ve had my LG condensing combo washer/dryer for about a year and a half.

Pros: I like that I can program the wash and dry cycles before leaving for work in the morning and come home to laundry ready to fold. After drying the machine goes into a cool down mode that lasts several hours, simply tumbling the laundry a few times every so often. There is no vent trap, although the rubber seal around the door does collect some lint. My understanding is that this type of drying removes less lint from the clothes, which supposedly is less damaging to the clothing. My clothes come out feeling very soft with no static cling. I can set the drying cycle to damp, normal, more dry, or choose dry times of 30 min or 1 hour.

Cons: The dry cycle is very noisy. It’s not a constant rumble noise, but an intermittent ronking mechanical sort of noise. We are in a very small home. Therefore, we try to always start our laundry on our way out the door. Of course this doesn’t allow particular items to be removed between the wash and dry cycles. The clothes do tend to come out wrinkled, some more than others. Jeans are the worst!

At this point I don’t know that I’d say a condensing (non-vented) dryer does a better job of drying, but I like it well enough to recommend it for someone trying to build an ultra tight home.

LH. We've had our whirlpool heat pump dryer for more than three years. It works fine. It does take longer to dry clothes, but not enough longer than a vented dryer to really matter. It's not any louder than a vented dryer. It's got a lot of options for various types of loads, so we can always find a combination of cycle, time and temperature that does what we need. I'd definitely get one if I had to do it again.

As for the earlier discussion about HRV noise, I guess one benefit of getting older is that I can't hear our Zehnder HRV in our bedroom, even on boost mode.

Bryce- I'd be interested in what brand of non-venting dryer you're experienced with. Ours gets clothes as dry as we want. Are you making a distinction between condensing dryers and heat pump dryers ( which also condense)?

Panasonic makes two ERV's to consider; one with 10, 20 and 40 CFM settings that installs like a large bathroom fan (WhisperComfort ERV FV-04VE1), and a second highly efficient traditionally ducted model that adjusts between 50-100 CFM (Intelli-Balance 100 FV-10VEC1). The Intelli-Balance model also has an ASHRAE timer to cycle the unit on and off if 50 CFM continuous is too much ventilation, to as little as 10 min/hr.

Either of these would be great choices for tiny houses, in my opinion. For example, 10 min/hr @ 50 CFM is the equivalent of running 8.3 CFM continuously, so the Intelli-Balance is essentially variable between 8.3-100 CFM.

An ERV also helps regulate indoor humidity by adding moisture to incoming air in the winter months and removing moisture from incoming air in the summer months (if your house is air conditioned). An HRV does neither, which can lead to over-drying the house in winter and adding excessive moisture during hot humid summer weather. Just like a passive make-up air damper. Food for thought.

I'm also looking for an HRV/ERV for a tiny house (200 sq ft) in Portland Oregon. Most of the HRVs are hugely oversized for a space like this. I had Zehnder design a system based around their smallest conventional HRV - ComfoAir 160 - however there was no way I was going to fit in all the required ducting, duct coupling units, silencers and so on. You're much larger at 720 sq ft, but I expect your issue would be all available space is already allocated to other things.
So the systems that fit my space are:
1. Zehnder ComfoAir 70. This would be the perfect unit for me. It is a through-the-wall unit however it can be configured with duct extensions run into up to 2 other rooms. So I would exhaust from the bathroom and supply into the living room. With this single extension configuration it's rated for 29 cu ft/min. It requires a min 10.8" thick exterior wall so in my case I would fur out the inside drywall as part of a shelving unit in the bathroom.
The problem with the 70 is that Zehnder is not actively marketing this right now. They're still working on certification issues. (Although it's fully certified and used all over Europe.) I'm presently trying to get an answer from Portland Bureau of Development Services whether they will approve this unit. Seems it's difficult though to get any indication ahead of time whether it would be approved. The way it seems to work is you install the unit, BDS tells you whether it's okay, and if it's not then I would deinstall it, install something else, and schedule another inspection. Because it involves a air barrier penetration I'm reluctant to go through this trial and error process.
2. Lunos eGo and e2 HRVs. Also through the wall units (11.8" or greater external wall thickness required.) So for my tiny home I would install a single eGo in the bathroom which just supplies/exhausts air in the bathroom. Then install either a single eGo in the living area, or an e2 pair doing push/pull.
These Lunos units are being actively sold and would almost certainly pass city inspection without any issues.
However for a number of reasons I don't think they're as advanced a design as the Zehnder ComfoAir 70. For one thing they're not based on a true enthalpy exchanger but instead deposit heat in a ceramic disc, then reverse the air flow to extract the heat back out of the disk. As someone mentioned above there will be this continual stop/reverse direction/start on the fans. Perhaps inaudible but I have no idea.
Using the Lunos units would also mean either 2 or 3 wall penetrations vs. only 1 for the Zehnder unit.
3. Zehnder ComfoSpot 50. These are like the Lunos eGo - a single unit that simultaneously extracts and supplies air from one vent / wall penetration. This appears to be a more advanced design than the comparable Lunos eGo, however it has the same issue as the ComfoAir 70: Zehnder is not actively marketing it as it's also pending certification.
So my conclusion right now is that there is an extremely limited number of of HRVs suitable for tiny houses with the best products in a kind or approval limbo.

I like your thinking however they will require me to have air exchange for the overall interior, not just in the bathroom.
The other thing is although BDS is a bit of a pain, I wouldn't go as far as to try to run around them. I'd rather continue to bother them until they tire of me and produce a decision on the Zehnder ComfoAir 70. I'm actually quite tenacious and eventually wore down Zehnder until they agreed to sell one to me.
One thing is that all these "tiny" HRV through-the-wall systems have different tube diameters. There is absolutely no standard. Actually both the Lunos eGo and e2 have a tube diameter of 162mm, the Zehnder 70 is 250mm and the Zehnder 50 is 315mm. This makes it difficult to just swap out one model and put in another. It would entail cutting a new hole and reflashing the sheathing.

Scott, I think that GBA article accurately describes the ComfoAir 70 and the other options available. The article is from 2016 however. Since then Zehnder sold a bunch of them apparently in Texas (presumably had an enthusiastic distributor there) but has subsequently stopped promoting them for a couple of reasons. They are still available "on-demand" as it were.
The natural course would be specify Lunos for tiny houses like everyone else presumably is. However the ComfoAir 70 is such a perfect fit for my structure that I'm doing what I can to make it happen.
What I'd really like to see is the City of Portland to say it's okay to install the ComfoAir 70 in Portland as the selection of suitable small HRVs is just way too small for the growing tiny house market. Of all places Portland really should be on to this.

Bill, last month I asked John Rockwell of Zehnder America about their spot ventilation options and this is what he wrote: "Im sorry to report we have discontinued the CA70 and the ComfoSpot50 was never available in the US market..."